Radio communication may take place between a communication device and a communication partner which may be a base station in a cellular communications network. Conventional designs for two-way communication include time-domain multiplexing and frequency-domain multiplexing, i.e. the transmission and the receipt of radio signals may take place either in different time frames or in different radio bands in order to avoid interference between the radio signals of the communication device and communication partner.
Using two different radio bands allows full-duplex communication, i.e. both communication partners may continuously transmit radio signals without causing signal interference. However, a most limited and valuable resource in radio communication is the spectral band used as a communication channel. Therefore, efforts have been made to simultaneously transmit and receive (STR) radio signals in the same frequency band. That approach has the potential of making double use of a given radio band but entails a technical challenge in that the (strong) radio signal transmitted by a communication device interferes with the (weak) radio signal received from a communication partner in the same frequency band.
In order to extract the radio signal originating from the communication partner, the self-interference caused by the own radio transmission of the communication device may be taken into account by the communication device receiving an overall radio signal in the frequency band shared by it and the communication partner. In a conventional attempt, the communication device may try to estimate or emulate or model the self-interfering signal and to subtract it from the received overall radio signal in the shared frequency band in order to obtain the radio signal emanating from the communication partner. That approach is referred to as self-interference cancellation (SIC).
Self-interference cancellation may be based on the fact that the communication device knows the radio signal that it is sending. That information may be used to purge the transmitted self-interfering radio signal from the received overall radio signal. However, the self-interfering radio signal may include at least one echo, i.e. the radio signal transmitted by the communication device may be reflected by some (unknown) object in the environment of the communication device. The interfering radio signal echo may return to the communication device with an (unknown) delay or phase shift. In order to take account of such a delayed self-interfering radio signal, the communication device may emulate a delayed radio signal component for the purpose of canceling it from the received overall radio signal.
Conventionally, a delayed radio signal component may be emulated in the communication device by guiding a copy of the radio signal through a delay line. However, as typical radio signal bands in mobile communication networks may be situated in a carrier frequency range from 2 GHz to 3 GHz (corresponding to wavelengths between 10 cm and 15 cm), delay lines tend to be excessively bulky with respect to spatial requirements of circuit integration and miniaturization with a view to building compact communication devices such as hand-held mobile devices.